Projection systems of various designs have been around for many years including projection systems called field sequential projection systems. In a field sequential projection system, single color lights are sequentially generated and projected through a spatial light modulator, such as a light valve, in order to generate a plurality of single color images. The color lights that are initially generated are single color lights typically associated with the primary colors of red, green, and blue. The single color images that are generated by the light valve, when projected onto a screen, may combine to form full-color images.
These field sequential projection systems can be categorized into at least two groups of field sequential projection systems, those that employ a single polychromatic light source such as those projection systems that employ color wheels and arc lamps, and those that employ multiple single color or monochromatic light sources. Examples of the second group include projection systems that employ light-emitting diodes (LEDs) to generate the different color lights.
When multiple single color light sources are employed in a field sequential projection system, each of the individual single color light sources are typically energized and de-energized sequentially. For example, if the single color light sources are used to generate the primary colors of red, green, and blue, each of the single color light sources will be sequentially energized and de-energized during nonoverlapping time periods. FIG. 1A depicts the ideal output waveforms generated by three single color light sources that generate the three primary colors of red (R), green (G), and blue (B). As depicted, in the ideal case, the output waveforms generated by each of the single color light sources will have instantaneous rise and fall times. Further, in such an ideal scenario, as soon as one light source is shut off, a second light source will be instantaneously turned on.
Unfortunately, output waveforms generated by single color light sources of conventional field sequential projection systems will not look like the output waveforms depicted in FIG. 1A but may instead have the output waveforms as depicted in FIG. 1B. The depicted output waveforms having gradual rise and fall times, which result in dead times between the output waveforms. The dead times between the output waveforms will mean that there will be a loss of lumens from the image or images that are projected onto the display screen.